Creep Test Flashcards
define creep
it is time dependent and permanent deformation of materials when subjected to a constant load or stress over a long period of time
creep usually occurs when
T>.4Tm
the temperature at which a material starts to creep depends on….
its melting point
displacement-limited applications
turbine rotors in jet engine
rupture-limited applications
high-pressure steam tubes and pipes
stress-relaxation- limited applications
suspended cables and tightened bolts
rate of creep depends on these following factors:
- materials properties
- exposure time
- exposure temperature
- applied load (stress)
what are the four stages of creep?
- instantaneous deformation-mainly elastic
- primary/transient creep-slope of strain vs time, decrease with time
- secondary/steady state-rate of straining is constant
- tertiary creep- rapidly accelerating strain rate up to failure
With either….. or …… the strain and steady state creep increases… the rupture lifetime is diminished
either increasing stress or temperature
what are some creep testing methods?
- tensile creep testing
- compressive creep testing
3 flexural creep testing
minimum steady state creep rate
slope of secondary portion of the creep curve. designed for long- life applications
rupture lifetime/time to rupture
time required till rupture.. for relatively short-life creep situations
creep modulus
ratio of intial applied stress to creep strain
creep strength/limit
it is the highest stress that a material can withstand for a specified length of time without exceeding the specified deformation at a given temperature
larson miller parameter is
T(C+logTr)
